Environmental, Industrial and Climatological Impacts of Internal Gravity Waves

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All naturally occurring fluids are stratified, meaning that their effective density decreases with height. The decrease can be rapid and localized, as at a thermocline in the ocean or at an atmospheric inversion. Or it can be gradual, as in the stratosphere. Propagating within such stratified fluids are internal waves, which move due to buoyancy forces. Because they transport energy and momentum and cause turbulence where they break, the waves have important consequences for climate, environment, air traffic, fisheries, offshore oil and other industries. However, relatively little is known about the dynamics of localized internal waves. Through three interrelated research streams, I propose to perform laboratory experiments and numerical simulations to develop predictive models for the evolution and breakdown of atmospheric and oceanic internal wave packets.***I will develop theory complemented by simulations to examine the response to flows induced by localized small amplitude wave packets. I have recently shown that, without breaking, vertically propagating wave packets launch long internal waves that redistribute the momentum of the packet over a wide horizontal extent.  Climate models, which use heuristics to predict momentum transport by internal waves, do not account for this effect and so incorrectly predict the spatial extent of the breaking region.  Including large-amplitude effects, I will examine the influence of the induced long waves upon the evolution of the wave packets themselves and will predict where winds are accelerated when two- and three-dimensional wavepackets ultimately break in the atmosphere.  This work will be applied to improve the representation of internal waves in climate models. I will also use this theoretical approach to predict mass transport by localized internal waves at a thick interface, with the intent of obtaining a better understanding of the lateral dispersion of pollutants and nutrients about the oceanic thermocline. Another research stream will examine the breakdown of internal wave packets at thick interfaces due to parametric subharmonic instability (PSI), a mechanism that has previously been examined only for periodic waves and more recently for wave beams. This more realistic examination of wave packet breakdown due to PSI will provide insight into the energy cascade from large to small scales, a result that will be cast for use in mixing parameterization schemes used in ocean general circulation models. A third research stream will perform laboratory experiments and simulations to examine the evolution of large amplitude interfacial internal waves as they shoal upon complex topography, with a focus upon energy redistribution, sediment resuspension and bedload transport. This work will be applied to assess hazards associated with the development and maintenance of offshore oil platforms and pipelines that run along the ocean floor.**